We carried out molecular dynamics simulations (MD) of heat conduction in Si with a nano-hole to represent the nano-structure, in order to investigate the mechanism of the thermal conductivity reduction of nano-structured materials. The Stillinger-Weber potential is used in this study. The temperature is kept constant at 300K by velocity scaling. Periodic boundary conditions are applied in the x, y and z directions. Phonon dispersion curves are calculated by using the time-space 2D Fourier transform. The phonon group velocity is calculated from the slope of the dispersion curve. The velocity is reduced by nano-holes, even if those are random. Phonon mean free path can be evaluated from the width of dispersion curve, and the long waves are clearly scattered by nano-holes. Phonon density of states (DOS) is also calculated by the Fourier transform of a velocity correlation. The DOS of Si with periodic nano-holes are slightly smaller than that of a single crystal Si. In other words, the specific heat is reduced by periodic nano-holes due to the reduced phonon modes. We discuss the mechanism of the reduction of the thermal conductivity of nano-porous material on the atomic scale.
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Numerical Calculation for Phonon Properties of a Nano-Porous Si
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Miyazaki, K, Nagai, D, Kido, Y, & Tsukamoto, H. "Numerical Calculation for Phonon Properties of a Nano-Porous Si." Proceedings of the ASME 2009 InterPACK Conference collocated with the ASME 2009 Summer Heat Transfer Conference and the ASME 2009 3rd International Conference on Energy Sustainability. ASME 2009 InterPACK Conference, Volume 1. San Francisco, California, USA. July 19–23, 2009. pp. 557-561. ASME. https://doi.org/10.1115/InterPACK2009-89118
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